Converting a cold water tank to a tropical

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Smithy26

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hello everyone, I have a 70L cold water fish tank with 4 goldfish in it. I am moving my gold fish to a different tank and was wondering if I would be able to change that tank to a tropical tank for fish such as guppies, platys etc.
If I am able to do this what will be required?
I do already have a thermometer and a heater big enough for the tank.
I appreciate any help or suggestions, Thankyou.
 
I did this 20 odd years ago. My first fish were my sons' fairground goldfish that grew so big we gave them to someone with a pond 9 months later. I did a big water change, put the heater in the tank to warm the water and bought tropical fish. Maybe I was lucky; 20 years ago I was just starting to keep fish and didn't really have a clue.


Before you do this, decide which tropical fish you intend. Do your research. Don't ask anyone at a fish shop as most of them will give poor advice.

Find out how hard your tap water is. Your water provider's website should have this information, you need a number and the unit of measurement (there are several) rather than some vague words. Fish have evolved in water of varying hardness. We need to keep fish that are from water with similar hardness to our tap water. The guppies and platies you mention are both hard water fish; they are fine if you have hard water. If you have soft water they will suffer so you would need soft water fish instead.

Once we know how hard your water is, we can suggest fish that will go together. Another aspect to stocking a tank whether different species have the same requirements. For example, fast swimming fish should not be kept in the same tank as slow moving fish as the fast swimmers will stress the slow swimmers just by being so active.

The website most of us use for research is https://www.seriouslyfish.com/knowledge-base/ This is just about the most reliable site out there, written by experts rather than someone who just keeps fish.
 
I’ve done this several times. When I upgrade and move my goldies to a bigger tank, I always move the tropicals to the old tank the goldies were in so they too can have a bigger tank. I just drain the water really low, vacuum the substrate very well and refill. I usually transfer some of the water they have been in also for stability. I add a heater and thermometer and once stable, I move the fish. I use the same filter and media that was already in there so the tank is already cycled. Never had a problem. I have drained the tank all the way down and changed substrate also. I just put the filter in the tank they are in at the time and let it keep running while I re-landscape.
 
As others have mentioned, all you need to do is clean the tank, filter, and gravel along with a significant water change, then add the heater. Get the temperature right and add a tropical fish or two. You should already have significant beneficial bacteria so cycling should not be an issue.
 
I have also done this several times without a problem just follow the information above and you will be fine. The big thing is to do your planning first so everything goes smoothly.
 
Thankyou everyone for all your help!
I have successfully converted my tank and am now housing guppies and platys!
 

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